Abstracts

The cortical areas that subserve language and handedness have been shown to undergo both intrahemispheric and interhemispheric reorganization in patients with brain injury or chronic partial epilepsy. The degree of cortical reorganization is strongly age dependent, being much more pronounced in children than in adults. We sought to identify the age beyond which cortical plasticity ceases to allow shifts in language dominance and handedness based on data from a large series of Intracarotid Amobarbital Procedures (IAPs).
We retrospectively reviewed data from 242 patients with medically refractory partial epilepsy who underwent the IAP as part of a comprehensive presurgical evaluation. We examined hemispheric language dominance, handedness, and age of seizure onset, and correlated these variables with the hemispheric lateralization of the epileptic focus (as assessed by Video-EEG monitoring and/or invasive intracranial EEG studies). For patients with left hemispheric foci, prevalence of right language dominance and left handedness were calculated within each age-of-onset group. An analogous analysis was performed on patients with right hemispheric foci.
Our patients aged from 7 to 66 years (mean 32.2 years, SD 11.8). Age of seizure onsets ranged from 0 to 51 years (mean 14.5, SD 10.8). We found that among patients with left sided epileptic foci, 23.11% (SD 4.49) of those whose seizure onset occurred before the age of 17.31 (SD 1.69) years, but only 4% (SD 5.70) of those with seizures started after that age were right language dominant. None of the patients with right-sided foci and seizure onset age of less than 18 years in our sample were right language dominant, whereas only 6.90% of those with right foci and seizure-onset age of later than 18 years showed right language dominance. In patients with left hemispheric foci, the percentage of left handed patients was 17.9% if seizure onset occurred before age 18 years and 13% if seizures started after that age. By comparison, in patients with right sided foci, 8.95% of those with seizure onset prior to age 18 years and 21.4% of those with seizure onset after age 18 years were left handed. When plotted using a moving window technique, we find a striking and abrupt change in the frequency of left handedness and right language between the ages of 15 to 19 years.
Our data indicate that maturation of both motor and language cortex occurs between the ages of 15 and 19 years. Before and, and after that age range, there was no significant variability in the prevalence of right language dominance in patients with left sided epileptic foci. In patients with right hemispheric foci whose seizures started before the age of18 years, left-handedness is slightly less than that for the general population. The presence of left hemispheric epileptic foci nearly doubles the odds of left handedness when seizures begin before the age of 18 years, but don[rsquo]t increase the likelihood of left-handedness beyond that age.